Wilkin was born on December 1, 1819 in Goshen, New York. His father Samuel J. Wilkin as well as his grandfather James W. Wilkin were politicians. Alexander studied law at Yale and became an attorney. In 1847, he joined the Tenth United States Army and became a captain. The army was deployed to Northern Mexico. Wilkin saw little action during his deployment, but gained a reputation as a serious soldier, and a man not to trifle with. However, on January 20, 1848, he shot and killed Joshua W. Collett in a duel. Despite his later regrets, he quoted that he "never felt cooler in his life".[1]

On March 6, 1848, he resigned his post and moved to Saint Paul, Minnesota Territory, in 1849. Two years later, President Millard Fillmore gave him the office of territorial secretary of the Minnesota Territory. The office was given to him presumably as a political favor (Wilkin was a Whig), and he served the office until 1853. While living in St. Paul, Wilkin invested in land, railroads, and newspapers. He worked as a lawyer and insurance agent. He also created the St. Paul Fire and Marine Insurance Company, the forerunner of what would become Travelers Insurance.

In October 1863, the Ninth Minnesota were sent to Missouri. The following May, the regiment marched to Memphis, Tennessee, and raised an army tasked with eliminating the threat that Nathan Bedford Forrest's cavalry was posing to the area. On June 10, 1864, Wilkin fought at the Battle of Brice's Crossroads which earned him praise for his bravery despite the Confederate victory. On July 14, 1864, he would face the battle that would come to be his last. Another expeditionary force decided to operate against Forrest. This force, operated by Wilkin, headed to Tupelo, Mississippi, where he was shot to death while speaking to another soldier. He was buried near where he fell, but his family recovered his remains and brought them to Goshen, where he was born. His father, Samuel Wilkin, outlived him by 20 months before he died in 1866. In 1868, Wilkin County, Minnesota, was formed as a way to honor the leader.[2] A statue of him was erected in the state capitol in 1910.